There are a number of great Instructables on LED grids out there. This is a low cost version - not quite as polished, but easy to make.
This project uses a couple of sheets of foam core, a fluorescent fixture cover from the local home store, a cut up strip of WS2812b LEDs, and an Arduino. All fairly inexpensive if you know where to get them (info below).Parts:
- LEDs - this project uses 25 LEDs, and there are a few choices here. For this one, a strip of WS2812b LEDs was used. There were 30 per meter in the strip I ordered, which makes soldering easier since they are farther apart. The 60/meter strips would also work. The 144/meter would not work since they only have one set of solder pads between each LED to allow them to be so close, and for this project, we are soldering wires between them all and need soldering pads on both sides. You could also use the WS2801 based strands, and those are typically pre-wired, making the project even easier. The other Instructables cover those pretty well, so this one will not go into more detail on those. Use non-waterproof or silicone jacketed (the jacket can be slid or cut off) strips. Avoid the epoxy waterproofed ones since you will need to clean that off of each end of each LED - doable, but unnecessary work if you order the other kind.
- Foam Core - 2 sheets, 20"x30", like these, though that link is 5x more than you need.
- Plastic cover - this is from the local home store and is used to cover fluorescent bulb fixtures. It's called an acrylic lighting panel, and the style is cracked ice. There are other possibilities here - the main thing is there is enough frosting to diffuse the LED light. Since the lighting panels are about 24"x 48", you can make two of these projects with one of them.
- Wire - each LED will have wires to connect to the next one - three wires between each. Hobby servo wire is nice to use since it's already three wires and color coded nicely.
- An Arduino Uno will do. Clone Arduinos are are available for about $10 each - a key for the low cost goal of this project. There are also smaller versions of Arduinos that would also work well for this project in that same price range. Older Arduinos will work fine too.
- Recommended - a power jack to supply 5 volts to the system. You can use the Arduino power and regulator if most of the LEDs are not on at the same time, but if they will all be on, the external 5 volts supply will avoid overheating the Arduino regulator. This jac will match your power supply - for me, it was a 2.1mm ID, 5.5 mm OD panel mount jack.